1. Field of the Disclosure
The present invention relates generally to semiconductor devices. More specifically, examples of the present invention are related to image sensors with enhanced blue light absorption.
2. Background
Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors, has continued to advance at great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
One type of image sensor, the complementary metal oxide semiconductor (CMOS) image sensor, is very popular in commercial electronics. However, as these semiconductor devices have scaled downward, photodiode area has also decreased resulting in a lower incident photon count on each photodiode. Several challenges for downscaled CMOS image sensors are maintaining low-light sensitivity and reducing image noise—two problems exacerbated by low a incident photon count.
Enhancing quantum efficiency and reducing cross talk are commonly accepted ways to improve CMOS image sensor performance as they may result in a more favorable signal to noise ratio. One way to improve quantum efficiency is to increase semiconductor thickness such that a photodiode can absorb more light before the light can penetrate the sensing volume. However, blue pixel quantum efficiency doesn't improve with increased semiconductor thickness, because this high-energy (short wave length) light is absorbed at the very surface of the semiconductor. Additionally, the typical light filter color choices (e.g. red, green, blue) block much of the blue light incident on the surface of CMOS devices, further limiting blue photon absorption.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.